1. Field of the Invention
The present invention relates to a backlight unit, and more particularly, to a backlight unit with a hybrid structure to improve heat-sink efficiency.
2. Discussion of the Related Art
The cathode ray tube (CRT) has been widely used as a display in televisions, measuring devices, and information terminals. However, the CRT cannot satisfy demands for miniaturization and light weight due to its inherent size and a weight. Thus, display devices such as a liquid crystal display (LCD) device using an electric field to cause an optical effect, a plasma display panel (PDP) using a gas discharge, and an electroluminescence display (ELD) device using an electric field luminous effect have been studied as a substitute for the CRT.
Among the display devices, the LCD device has been most actively studied, so the LCD device having beneficial characteristics such as compact size, light weight, and low power consumption have been highly developed for ultra-thin flat display devices, for example, monitors for spacecraft, aircraft, notebook computers, laptop computers, desktop computers, and large-sized display devices. That is, the demand for the LCD devices has continuously increased.
Generally, the LCD device includes an LCD panel for displaying a picture image and a driving device that applies a driving signal to the LCD panel. The LCD panel includes first and second glass substrates bonded to each other with a predetermined distance inbetween, and a liquid crystal layer formed between the first and second glass substrates.
The first glass substrate (TFT array substrate) includes a plurality of gate and data lines, a plurality of pixel electrodes, and a plurality of thin film transistors. At this time, the plurality of gate lines are formed on the first glass substrate at fixed intervals, and the plurality of data lines are formed substantially perpendicular to the plurality of gate lines at fixed intervals. Then, the plurality of pixel electrodes, which are arranged in a matrix configuration, are respectively formed in pixel regions defined by the plurality of gate and data lines crossing each other. The plurality of thin film transistors are switched according to signals on the gate lines to transmit signals of the data lines to the respective pixel electrodes.
The second glass substrate (color filter substrate) includes a black matrix layer that excludes light from regions except the pixel regions of the first substrate, a R(red)/G(green)/B(blue) color filter layer displaying various colors, and a common electrode to obtain the picture image.
Next, a predetermined space is maintained between the first and second glass substrates by spacers, and the first and second substrates are bonded to each other by a seal pattern having a liquid crystal injection inlet. Also, the liquid crystal layer is formed between the first and second glass substrates by injection of liquid crystal.
Meanwhile, the LCD device controls the transmittance of light to display the picture image. In this respect, the LCD device requires an additional light source such as a backlight unit. The backlight unit is classified into a direct-type method and an edge-type method according to a position of a lamp unit.
The LCD device uses a light source such as an Electro Luminescence (EL), a Light Emitting Diode (LED), a Cold Cathode Fluorescent Lamp (CCFL), or a Hot Cathode Fluorescent Lamp (HCFL).
In the edge-type method, the lamp unit is formed at one side of a light-guiding plate. The lamp unit includes a lamp, a lamp holder, and a lamp reflecting plate. The lamp is inserted into both sides of the lamp holder, whereby the lamp holder protects the lamp from an external impact. Also, the lamp reflecting plate reflects the light emitted from the lamp to the light-guiding plate.
Generally, the edge-type method of providing the lamp unit at one side of the light-guiding plate is applied to relatively small sized LCD devices such as the monitors for the laptop type computer or the desktop type computer. The edge-type method is useful to obtain uniform luminance, long lifetime and thin profile in the LCD device.
With the trend to large-sized LCD devices of 20-inches or more, the direct-type method has been developed, in which a plurality of lamps are formed in one line on a lower surface of a light-diffusion plate, whereby the entire surface of the LCD panel is directly illuminated with the light. The direct-type method, which has greater light efficiency as compared with that of the edge-type method, is used for large-sized LCD devices requiring high luminance.
Hereinafter, a related art backlight unit will be described with reference to the accompanying drawings.
FIG. 1 illustrates a perspective view of a backlight unit according to the related art. FIG. 2 illustrates a rear view of a backlight unit having a heat-sink plate according to the related art. FIG. 3 illustrates a cross sectional view, along I-I′ of FIG. 1.
FIGS. 1, 2, and 3 illustrate a related art direct type backlight unit. The related art backlight unit includes a cover bottom 10, a plurality of fluorescent lamps 11, a metal PCB. 12, and a plurality of R/G/B LED lamps 13. At this time, the plurality of fluorescent lamps 11 are oriented in one direction inside the cover bottom 10. The metal PCB 12 adheres to an inner bottom of the cover bottom 10. The plurality of R/G/B LED lamps 13 are formed in one direction, wherein each of the LED lamps 13 is provided between the fluorescent lamps 11 or on the metal PCB 12. The metal PCB 12, on which the LED lamps 13 are mounted, is formed of aluminum which has great thermal conductivity.
In the above-mentioned backlight unit according to the related art, the fluorescent lamps 11 and the LED lamps 13 are formed together, which is referred to as a hybrid structure.
If using the LED lamps 13, it is necessary to provide a heat-sink plate because the LED lamps 13 emit a large amount of heat. Thus, if the heat-sink plate is not provided in the backlight unit using the LED lamps 13, the lifetime of backlight unit becomes shorter and the heat-sink efficiency of backlight unit is lowered.
In more detail, heat-sink plates 14 are formed at the rear side of the cover bottom 10, for emission of the heat generated from the fluorescent lamps 11 and the LED lamps 13. The heat-sink plates 14 adhere to a rear surface of the cover bottom 10 corresponding with the metal PCB 12. In this case, the heat generated from the fluorescent lamps 11 and the LED lamps 13 is transmitted to the outside through the metal PCB 12, the cover bottom 10, and the heat-sink plates 14.
If the heat-sink plates 14 directly adhere to the rear surface of the cover bottom 10, the cover bottom 10 serves as a heat resistance, whereby it is difficult to effectively transmit the heat to the outside.